Crystal engineering studies the design and synthesis of solid-state structures with desired properties through deliberate control of intermolecular interactions. It is an interdisciplinary academic field, bridging solid-state and supramolecular chemistry.

The main engineering strategies currently in use are hydrogen- and halogen bonding and coordination bonding. These may be understood with key concepts such as the supramolecular synthon and the secondary building unit.

The term 'crystal engineering' was first used in 1955 by R. Pepinsky but the starting point is often credited to Gerhard Schmidt in connection with photodimerization reactions in crystalline cinnamic acids. Since this initial use, the meaning of the term has broadened considerably to include many aspects of solid state supramolecular chemistry. A useful modern definition is that provided by Gautam Desiraju, who in 1988 defined crystal engineering as "the understanding of intermolecular interactions in the context of crystal packing and the utilization of such understanding in the design of new solids with desired physical and chemical properties." Since many of the bulk properties of molecular materials are dictated by the manner in which the molecules are ordered in the solid state, it is clear that an ability to control this ordering would afford control over these properties.

Crystal engineering relies on noncovalent bonding to achieve the organization of molecules and ions in the solid state. Much of the initial work on purely organic systems focused on the use of hydrogen bonds, although coordination and halogen bonds provide additional control in crystal design.

Molecular self-assembly is at the heart of crystal engineering, and it typically involves an interaction between complementary hydrogen bonding faces or a metal and a ligand. "Supramolecular synthons" are building blocks that are common to many structures and hence can be used to order specific groups in the solid state.

The intentional synthesis of cocrystals is most often achieved with strong heteromolecular interactions. The main relevance of multi-component crystals is focused upon designing pharmaceutical cocrystals. Pharmaceutical cocrystals are generally composed of one API (Active Pharmaceutical Ingredient) with other molecular substances that are considered safe according to the guidelines provided by WHO (World Health Organization). Various properties (such as solubility, bioavailability, permeability) of an API can be modulated through the formation of pharmaceutical cocrystals.

2D architectures (i.e., molecularly thick architectures) is a branch of crystal engineering. The formation (often referred as molecular self-assembly depending on its deposition process) of such architectures lies in the use of solid interfaces to create adsorbed monolayers. Such monolayers may feature spatial crystallinity. However the dynamic and wide range of monolayer morphologies ranging from amorphous to network structures have made of the term (2D) supramolecular engineering a more accurate term. Specifically, supramolecular engineering refers to "(The) design (of) molecular units in such way that a predictable structure is obtained" or as "the design, synthesis and self-assembly of well defined molecular modules into tailor-made supramolecular architectures".

Scanning probe microscopic techniques enable visualization of two dimensional assemblies.